Air propeller



April 4, 1939. 1.. HOFFMANN 2,152g805 AIR PROPELLER Filed Nov. 2, 1957 Patented Apr. 4, 1939 UNITED, STATES AIR PROPELLEB Ludwig Hoflmann, Berlln-Hermsdorl, Germany,

assignor to Gustav Schwarz Kommanditgesellschaft, Berlin, Germany, a German company Application November 2, 1937. Serial No. 172,861

In Germany November 4, .1936 p 3 Claims. (01. 1'l0'159) My invention relates to improvements in air propellers, and more particularly in air propellers of the type in which a blade of wood is fixedin a cylindrical metallic sleeve mounted on 5 the hub. In constructions now in use the root of the blade is formed with screw-threads engaging in corresponding screw-threads made within the said sleeve, a suitable binding medium 1 such as putty or cement being used for rigidly fixing the root to the blade. The object of the improvements is to prevent the access of moisture and dust into the annular space formed be-, tween the outer portion of the sleeve and the root of the blade, which moisture andpdust tend.

to spoil the Wooden blade, and with this object in view my invention consists in providing pack- =ing means at the end of the sleeve and between j the same and the root of the blade. Such packing means are particularly important in pro- 2 pellers in which the blade is provided with a moisture proof coating such as is ordinarily made from lacquer or a cellulose derivative. Such coatings cannot be extended into the sleeve and to the part of the root which is fixed thereto, and

2 therefore an unprotected part is produced between the said joint and the coated 'portion of the blade and root, to which moisture and air have access. In my improved propeller this objection is obviated.

In the preferred construction the sleeve is extended outwardly beyond the joint of the root of the blade, and the packing medium is confined between the said extension and the root. In

this case the coating of the blade extendsfin'to 4 able binding medium interposed between the same. and it has a protective coating b which is made for example from a cellulose derivative, and which,is proof as against moisture and mechanical attack by water, sand or gravel. The inner end it of the root of the blade is formed with screw-threads engaging in corresponding screwthreads e of. a sleeve c, the said sleeve being mounted on the hub of the propeller. The joint is made rigid by means of a suitable binding medium or cement applied between the screwthreads of the sleeve and the root.

In the example shown in the figure the sleeve 0 is extended outwardly beyond the said joint, as is shown at h, and the said extension is formed internally with a circumferential cavity 1 adapted to receive a suitable packing medium g. The protective coatingb extends from the body of the blade into the outer portion of the sleeye c and to a part near the joint d, e, so that it is embraced by the packing medium 9 and access of moisture and dust to the inner portions of the root of the blade is prevented. The outer end i of the sleeve has a certain play relatively to the root of the blade so that no' transverse pressure is exerted on the said outer end of the sleeve by the oscillations and other deformation of the blade caused in service. For the same reason I prefer to make the packing g from elastic material, a .ring or strips of rubber wound around the root of the blade being preferred. From the foregoing description of the invention it will be understood that access of moisture and dust tothe inner portion of the sleeve and to the unprotected inner part of the root is prevented.

While in describing the invention reference has been made to, an example in which the propeller blade is provided at its root with a protective coating, and in which the pacln'ng medium is locatedwlthin an extension of the sleeve, 1 wish it to be understood that my invention is not limited to these features.

I claim:

1. The herein described propeller, comprising a blade composed of a metallicsleeve, the portion of said root located within said sleeve having a surface permitting the access of humidity into the same, a body made from non-metallic material having its root permanently fixed within said sleeve, and a packing medium in position for preventing access of foreign matter to the' inner part of said sleeve and the said root.

2. The herein described propeller comprising a blade composed of a metallic sleeve, a body made from non-metallic material having its root permanently fixedwithin said sleeve and provided with a protective coating extending from the outer part of said body into the outer portion of said sleeve and leaving the inner part of saidroot bare, and a packing medium between said sleeve and protective coating preventing access of foreign matter into the sleeve.

3. The herein described propeller comprising a blade composed of a sleeve, a body made from wood permanently fixed with its root within said sleeve, said sleeve having an extension beyond the joint of said body formed internally with a circumferential cavity and having clearance around the root of the blade, a. protective coating on said body extending in said extension to the 

